Nullable string type hinting gives syntax error in PHP 7.2

Question

I'm using PHP 7.2 and trying to type hint this variable:

class TestClass
{
    public static ?string $test = null;

But PHP gives me the following error:

syntax error, unexpected '?', expecting function (T_FUNCTION) or const (T_CONST)

And I'm absolutely clueless why! Am I doing something wrong?

Answer 1

Typed properties were not included until PHP 7.4.